Recall the linked-node implementation of a queue, where:
The first element of the header (index 0) points to the head (start) of
the queue
The second element of the header (index 1) points to the tail of
the queue
Each element (node) of the queue is linked to the element behind it
We define convenience functions, that are not part of the queue ADT, to
make it easier to implement the ADT.
These functions facilitate accessing and setting parts of the queue
header structure.